Authors: Riccardo Serra; Noah Leviton Gorelick; Riccardo Serra, MD; Arba Cecia; Rajiv Iyer, MD; Betty Tyler; Mark Gregory Luciano; Henry Brem, MD (Baltimore, MD)

Introduction: While both differential pressure and resistance valves have been used alone and in combination to regulate flow in shunting, the resultant flow is not well understood. In our benchtop gravity-flow system, here using Certas+ and Hakim valves with Siphonguard, we vary protein content, temperature and pressure in diurnal simulations of upright and supine conditions to evaluate CSF flow rate and variability. Methods: Saline and Human CSF were tested for 2 consecutive trials of 30 days each. CSF was collected from patients through an IRB-approved protocol and filtered, protein concentration was adjusted to 500 mg/dl. Hourly measurements of ICP, temperature and flow output collected for both upright and supine positions of the Certas and Hakim valves, thereby varying resistance and ball valve engagement. Flow rates were calculated and plotted using set valve resistances (3 Certas+ at 2, 3 Hakim valves at 50) allowing for comparison between saline and high-protein CSF, and temperature (25°and 37° C). Results: Protein effect: when tested supine with high-protein CSF at 37° C, Certas+ valves went from 37 ml/hr to 27 ml/hr (37% increase, p=0.01), compared to protein-free saline, with no increase seen in the upright position. Hakim valve supine flow increased (52 ml/hr Vs 38 ml/hr, 36.8%, p=0.07) and upright positions (27 ml/hr Vs 22 ml/hr, 22%, p=0.02). Temperature effect: With higher temperature valves showed a increased CSF flow rates when the temperature was raised, 20% (p=0.004) and 55%, (p=0.001). in Hakim and Certas+ valves, respectively. Conclusion: CSF (with protein) and temperature interact to increase the flow rate and variability through valve systems. These effects are different in different ball valves constructs and especially different comparing ball valve to resistance regulation. Further, these changes are in the range that have potential clinical impact.